Tropical Storm ISAAC

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TROPICAL STORM ISAAC DISCUSSION NUMBER 28
NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012
1000 PM CDT MON AUG 27 2012
THE SATELLITE PRESENTATION OF ISAAC HAS NOT CHANGED VERY MUCH DURING
THE PAST FEW HOURS. INFRARED AND MICROWAVE IMAGERY SHOW A STRONG
BAND OF CONVECTION...PERHAPS THE BEGINNING OF AN EYEWALL...WRAPPING
AROUND THE SOUTH AND EAST PORTIONS OF THE CIRCULATION. HOWEVER...
AIRCRAFT OBSERVATIONS INDICATE THAT THE CONVECTIVE BAND WAS OPEN TO
THE NORTHWEST AND THAT THE LOW-LEVEL CENTER WAS DISPLACED A LITTLE
TO THE SOUTH OF THE ROTATION SEEN IN SATELLITE PICTURES. THE
MINIMUM PRESSURE HAS NOT FALLEN SIGNIFICANTLY DURING THE PAST
SEVERAL HOURS AND THE NOAA AND AIR FORCE AIRCRAFT HAVE NOT REPORTED
WINDS ANY HIGHER THAN WHAT WAS MEASURED LATE THIS AFTERNOON.
THEREFORE...ISAAC REMAINS A 60-KT TROPICAL STORM FOR THIS ADVISORY.
ISAAC CONTINUES TO HAVE DIFFICULTLY MAINTAINING DEEP CONVECTION
OVER THE NORTHERN SEMICIRCLE LIKELY DUE TO SOME DRY AIR
ENTRAINMENT. OTHERWISE...ENVIRONMENTAL CONDITIONS SHOULD BE
CONDUCIVE FOR STRENGTHENING UNTIL LANDFALL. ISAAC IS FORECAST TO
BECOME A HURRICANE OVERNIGHT AND NHC INTENSITY FORECAST IS SLIGHTLY
HIGHER THAN MOST OF THE GUIDANCE.
ISAAC HAS BEEN MOVING NORTHWESTWARD OR 310 DEGREES AT 9 KT. THE
TRACK GUIDANCE HAS CONTINUED TO COME INTO BETTER AGREEMENT DURING
THE FIRST 36 TO 48 HOURS OF THE FORECAST PERIOD. ISAAC SHOULD MOVE
NORTHWESTWARD TOWARD THE NORTH-CENTRAL GULF COAST WHERE A BREAK IN
THE SUBTROPICAL RIDGE IS LOCATED. AS A MID-LATITUDE TROUGH
BYPASSES ISAAC IN A DAY OR SO...SOME RIDGING BUILDS TO THE
NORTHWEST OF THE CYCLONE. THIS IS EXPECTED TO CAUSE ISAAC TO
SLOW DOWN AS IT MOVES INLAND. AFTER 72 HOURS...THE CYCLONE SHOULD
BEGIN TO MOVE A LITTLE FASTER TOWARD THE NORTH AND NORTHEAST AS IT
MOVES AROUND THE WESTERN SIDE OF A MID-LEVEL RIDGE THAT SLIDES
EASTWARD ACROSS THE OHIO VALLEY AND MID-ATLANTIC REGIONS. THE NEW
NHC TRACK IS SIMILAR TO THE PREVIOUS ADVISORY AND REMAINS BETWEEN
THE ECMWF AND GFS MODELS.
ISAAC IS A LARGE TROPICAL CYCLONE. A DANGEROUS STORM SURGE...HEAVY
RAINFALL...AND STRONG WINDS EXTEND WELL AWAY FROM THE CENTER AND
ARE EXPECTED TO AFFECT A LARGE PORTION OF THE NORTHERN GULF COAST.
THE THREAT OF HEAVY RAINFALL AND FLOODING IS ALSO EXPECTED TO
SPREAD INLAND OVER THE LOWER MISSISSIPPI VALLEY REGION DURING THE
NEXT FEW DAYS.
FORECAST POSITIONS AND MAX WINDS
INIT 28/0300Z 27.1N 87.0W 60 KT 70 MPH
12H 28/1200Z 28.0N 88.0W 70 KT 80 MPH
24H 29/0000Z 29.1N 89.2W 80 KT 90 MPH...ON THE COAST
36H 29/1200Z 29.9N 90.1W 65 KT 75 MPH...INLAND
48H 30/0000Z 30.7N 90.7W 50 KT 60 MPH...INLAND
72H 31/0000Z 33.3N 91.7W 30 KT 35 MPH...INLAND
96H 01/0000Z 37.5N 91.5W 25 KT 30 MPH...POST-TROP/REMNT LOW
120H 02/0000Z 40.5N 87.5W 20 KT 25 MPH...POST-TROP/REMNT LOW
$$
FORECASTER BROWN/BLAKE
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